Method for determining the operability of a source range detector

Abstract

A method of determining the operability of a source range detector located adjacent a nuclear reactor in which the source range detector generates a count corresponding to the neutrons emitted by the reactor when the reactor is operating within the source range and a predetermined voltage is applied across the electrodes of the detector, the detector being subject to destruction when the reactor power level is above the source range and the predetermined voltage is applied across its electrodes. The method includes the steps of: (a) operating the reactor at a power level above the source range; (b) applying a voltage across the electrodes of the detector, the voltage having a magnitude below that necessary to generate a neutron count from the detector; (c) gradually increasing the magnitude of the voltage across the electrodes of the detector until the detector just begins to generate a neutron count; (d) reducing the voltage across the electrodes of the detector; and (e) replacing the detector if a neutron count is not generated in step (c) at a voltage having a magnitude less than the predetermined voltage.

I claim: 
     
       1. A method of determining the operability of a source range detector which is only operable in the source range of a nuclear reactor and which is located adjacent such a nuclear reactor, said source range detector registering a count corresponding to the neutrons emitted by the reactor when said reactor is operating within said source range and a predetermined operating voltage is applied across the electrodes of said detector, said detector being subject to destruction when said reactor power level is above the source range and said predetermined voltage is applied across its electrodes, said method comprising the steps of: (a) operating said reactor at a power level above said source range;   (b) applying a voltage across the electrodes of said detector which does not cause said detector to register a neutron count;   (c) gradually increasing the magnitude of the voltage across the electrodes of said detector until said detector registers a neutron count;   (d) reducing the voltage across the electrodes of said detector; and   (e) replacing said detector if a neutron count is not registered in step (c) at a voltage having a magnitude about said predetermined operating voltage magnitude.   
     
     
       2. A method as claimed in claim 1 which further comprises the step of calibrating the detector by recording the voltage magnitude at which the detector registers a neutron count and thereafter repeating steps (a), (b), (c) and (d), said method additionally including the steps of comparing the voltage magnitude of the repeated steps at which the detector registers a neutron count with said recorded voltage magnitude and using the difference in voltage magnitudes as a measure of the operability of the detector. 
     
     
       3. A method as claimed in claim 1, including automatically carrying out steps (a), (b), (c) and (d) on a periodic basis. 
     
     
       4. A method as claimed in claim 1 which comprises the further step of activating an alarm if the detector does not register a neutron count at a voltage across the electrodes which is equal to or lower than said predetermined operating voltage magnitude. 
     
     
       5. A method of determining the operability of a source range detector which is only operable in the source range of a nuclear reactor and which is disposed in the vicinity of a nuclear reactor which is operating at a power level above the source range, the detector having electrodes and producing a current corresponding to a count of neutrons detected by the detector when a voltage is applied across its electrodes, comprising: gradually increasing the voltage across the electrodes from a magnitude which does not cause said detector to produce a current corresponding to a neutron count to a magnitude at which the detector does produce such a current;   lowering the voltage to a magnitude which will not produce a current through the detector that would damage the detector at the highest power level of the reactor; and   replacing the detector with an operable detector if the detector does not generate a current corresponding to a neutron count when the voltage across the electrodes reaches the rated maximum operating voltage of the detector, signifying that the detector is defective.   
     
     
       6. A method as claimed in claim 5 which further comprises the step of calibrating the detector by recording the voltage at which the detector first generates a current corresponding to a neutron count and thereafter repeating said increasing and lowering steps, said method additionally including the steps of comparing the voltage of the repeated steps at which the detector first generates a current corresponding to a neutron count with the recorded voltage and using the voltage difference as a measure of the operability of the detector. 
     
     
       7. A method as claimed in claim 5, wherein said increasing and lowering steps are automatically performed in sequence on a periodic basis. 
     
     
       8. A method as claimed in claim 5 which further comprises the step of activating an alarm if the detector does not generate a current corresponding to a neutron count at a voltage across the electrodes which is equal to or lower than the rated maximum operating voltage of the detector.